Overvoltage surges, which travel along an electric power distribution system and which are not properly averted or diverted, often damage transformers and other electrical equipment of the electric power distribution system, as well as the electrical equipment of residential, commercial and industrial customers supplied by the electric power distribution system. Consequently, surge arresters are commonly used in an electric power distribution system for shunting overvoltage surges to system ground before the overvoltage surges can damage the electrical equipment connected in, or to, the electric power distribution system.
Typical surge arresters used in electric power distribution systems can fail in a runaway condition. When such a failure occurs, the surge arrester may explode apart, potentially damaging nearby equipment and injuring anyone who happens to be near. Therefore, it has been a common prior art practice to provide surge arresters with fault disconnectors which open the circuits containing failed surge arresters. Usually, a fault disconnector is connected between its corresponding surge arrester and ground so that, when the fault disconnector activates upon failure of the surge arrester, the fault disconnector separates the surge arrester from its ground connection. The separated ground connection not only disconnects the failed surge arrester from the electric power distribution system, but also provides a visible indication to a utility linesmen that the surge arrester has failed.
A typical fault disconnector includes a cartridge, which may contain a predetermined amount of gun powder, and which is heated as the surge arrester begins to fail. When the cartridge heats sufficiently, it explodes separating the surge arrester from its ground connection. The amount of gun powder that is used in the cartridge is sufficient to cause such separation but not sufficient to cause damage or injury.
The cartridge, and the other elements of the fault disconnector, are contained within a disconnector housing that is a separate component of the surge arrester, that has an internally threaded hole for threaded attachment to a housing of the surge arrester, and that has an external threaded ground connector for attachment to a ground lead. An electrical resister, which is another element of the fault disconnector and which is housed by the disconnector housing, is electrically connected between a surge arrester terminal and the ground connector of the disconnector. Accordingly, when the surge arrester fails, the current through the electrical resister increases abnormally and generates enough heat to trigger the cartridge causing it to break the disconnector housing and to separate the ground terminal from the surge arrester.
The use of a separate disconnector housing increases the part count of a surge arrester which, in turn, increases the manufacturing cost of the surge arrester. The present invention is directed to a surge arrester which reduces part count.